Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, for example, to an image processing apparatus and an image processing method for controlling a placement amount of color material.
Description of the Related Art
Presently, image processing apparatuses such as multi function machines and printers for printing image data sent from an input unit such as a host computer or an image scanner are widely used.
In image processing apparatuses using an electrophotographic system, first, a photosensitive drum is evenly charged with a charging roller etc. After that, in accordance with an image signal generated based on the image data, for example, by exposing the photosensitive drum with laser light from a laser scanner, an electrostatic latent image is formed on the photosensitive drum. The formed electrostatic latent image is developed with a developing unit, and the developed toner image is transferred to a material to be transferred by a transfer roller etc. Then, the toner image becomes fixed to the material to be transferred by a fixing unit to thereby enable the image to be printed.
In contrast, when a large amount of adhering toner (that is, the toner placement amount is large) in the development, there may occur such trouble that the toner is not completely fixed and scatters, or the toner drops out in a part having a high dot density. It is known that such trouble occurs with different frequencies according to such environmental conditions as humidity and/or temperature in which the image processing apparatus is placed. Moreover, there are various kinds of media used for printing such as paper, and similar troubles also occur occasionally depending on the kind of the medium.
Furthermore, there has been occurred a problem that, when a straight line is printed in a main scanning direction, the toner scatters to rearward of the line recorded on the material to be transferred in a sub scanning direction (paper feed direction) to thereby deform the image. This is caused by the generation of vapor due to moisture in the material to be transferred by rapid temperature rise when the material to be transferred passes through the fixing unit. This is because, when the toner placement amount is large at this time, the vapor in the material to be transferred is trapped and such phenomenon occurs in which the vapor blows off the toner to rearward of the feed direction. Hereinafter, such phenomenon in which the toner scatters to rearward in the sub scanning direction for the straight line image in the main scanning direction to thereby deform the image is described as a tailing phenomenon.
As a countermeasure against such tailing phenomenon, conventionally, such method is adopted as decreasing the adhesion amount of toner. Specifically, the tailing phenomenon is apt to occur in an image region having specified features. Accordingly, by extracting an image region having such features and performing thinning processing on the image data of the extracted image region, the adhesion amount of toner was able to be decreased with a reduced adverse effect on the image quality (for example, Japanese Patent Laid-Open No. 2004-314308).
In Japanese Patent Laid-Open No. 2004-314308, in order to extract the image region having the specified features, input image data to be a processing object is converted into a binary image, and an edge determination of a solid image region is performed to determine whether or not the image region of a target pixel is an object region of the processing. Furthermore, regarding the extraction of the image region, in Japanese Patent Laid-Open No. 2009-152766, by obtaining the binarization threshold from the density of a peripheral pixel of the target pixel, the image data of the processing object is expanded to a multi-value image.
In contrast, when input data are image data read with an image scanner, the extraction of an effective image region by a conventional edge determination is difficult. This is because, edge parts of image data read with an image scanner do not have straight lines but lines having unevenness. Moreover, since there is variation in density distribution inside the edge, conventional extraction processing of an image region was not able to extract precisely the image region to be a processing object. In Japanese Patent Laid-Open No. 2009-139664, in order to solve these problems, an extract processing of an image region is performed in accordance with the result of the edge determination, and then the thinning processing on the extracted region is performed, when the input data are image data received from the outside such as a host computer. In contrast, by weakening a direct-current component of development bias, development properties are lowered and the adhesion amount of toner is reduced, when the input data is an image data read with an image scanner.
In Japanese Patent Laid-Open No. 2009-152766, in order to convert image data to be a processing object into a multi-value image, the binarization threshold is estimated from the density of peripheral pixels of the target pixel, and, after subjecting the multi-value image to a binarization processing, edge determination processing similar to that for a binary image is performed. However, the calculation of the optimum threshold requires a large processing load, and, in particular, realization of determination processing with a practical processing speed through the use of software is difficult.
In Japanese Patent Laid-Open No. 2009-139664, reduction processing of a toner adhesion amount is changed between image data read with an image scanner and the other image data. However, recently, there is such case where an image read with an image scanner is once sent to a host computer, and the image read with the image scanner is sent from the host computer to an image processing apparatus and is printed. In such a case, although the input image data are image data taken in with an image scanner, the data are image data input from an external device, and thus appropriate extraction processing of the image region was not able to be performed.